In a local area network based upon IEEE 802.11 stations can enter a power save state. When in a power save state, the station (STA) will wake up in order to receive a beacon from the network controller; an access point (AP) in the case of an infrastructure network or group owner (GO) in the case of Wi-Fi Direct. Generally when a STA is in the power save state and sleeping, the AP or GO buffers packets for that STA and then indicates in the beacon if there are buffered packets for that STA. By waking up for beacons, the STA can then determine if there are buffered packets for it and can then retrieve them. In newer schemes for devices that sleep for long periods the STA may wake and contact the AP without waiting for a beacon.
In a local area network based upon DECT Ultra Low Energy (ULE) as per ETSI TS 102 939-1, the network generally consists of a DECT ULE Base Station (BS) and several DECT ULE devices (UDs). The UD is generally a battery powered device that is intended to sleep for long periods. When the UD wakes, it needs to first synchronize with the BS and then can either send data to the BS or simply send a single null data packet in order to pull any data from the BS that is intended for the UD.
In both of the examples given above, the network controller, FP (Fixed Part), i.e. the AP or BS, must buffer any packets intended for any and all of the sleeping clients, PP (Portable Part), i.e. STA or UD, until the client wakes and contacts it. The message or messages for one or more PPs is sent to the FP from an application that is either local on the distribution system or remote over the internet, for example. Therefore the controller must have the capacity to store all of the messages that are for sleeping clients until each client wakes and contacts the controller. In networks where there are a large number of clients, the controller requires more and more memory capacity. Hence, in networks that consist of many sensor or activator devices, such as is found in security, control, energy management, telemetry, etc. the number of clients can be large and the amount of storage high. Some controllers, such as a DECT ULE Base Station or a small or ‘soft’ AP are not usually designed to have high storage. In addition, the traffic for the clients can often be very intermittent with sudden spikes in activity as, for example, when all the clients are required to be re-configured or particular data is required from many devices within a short time span. It is difficult to estimate the message sizes, the distribution of the messages or the time required to store the messages. All this requires a ‘worse case’ estimate and hence potentially large, expensive storage. Another potential problem is that if many clients contact the controller within a short period, then they compete and each needs to stay awake until they receive their data. This can be inefficient as the wake time on average for each client is increased as each must wait until other clients are first serviced. Furthermore, if the network is shared with clients that have higher throughput requirements, then the air time consumed by the sleeping client waking up for messages and data can become significant and reduce the overall capacity of the network.
There is a growing need to reduce the buffering of many messages in the controller and to reduce the time that clients need to be awake, thereby improving the efficiency of the network and the power consumption of the devices.